The general construction of a sealed, cylindrical cell is such that its principal components, an anode and a cathode, are assembled into a can, together with the appropriate separators, electrolyte, etc, and the cell is then closed by a seal placed in the open end of the can. The seal precludes electrolyte leakage from the cell, and insulates the electrode contacts of the cell from each other.
A seal will desirably also permit hydrogen gas permeation from the cell so as to reduce pressure build-up within the cell, and yet also to inhibit moisture gain or loss, and oxygen or carbon dioxide infiltration into the cell. Still further, the seal is usually manufactured with a molded-in membrane or thin section so as to assure that the cell will vent under certain conditions when high gas pressure buildup within the cell may occur, and to preclude rupture of the cell.
The ability of sealing and insulating members to serve the purposes and functions of sealing and insulating sealed galvanic cells, may be very often determined simply by appropriate testing methods, whereby a number of cells may be subjected to discharge and charging tests, short circuit tests, temperature cycling, high or low temperature longlife storage testing, and so on. Some seals may pass certain of the tests very well, but be somewhat less consistent on other tests; and although nearly all of the tests are quite extreme, they are indicative of the kinds of use and abuse conditions that may exist in the field. Many commercially used sealing and insulating members for cells have passed many tests, but the provision of sealing and insulating members that can pass all of the tests consistently, and at the same time permit installation of more active material in the cell, provides greater assurance of consistent performance in the field. Moreover, as will be discussed hereafter, considerable economies of supply and manufacture may be effected by the present invention.
The present invention is directed toward seals which may be snap-fitted or snap-fittable when placed in cells with assurance that they will remain in place, even on high speed cell assembly lines. Moreover, the present invention provides seals that are supported by a metal disc, providing a stronger structure, and which may be easily and inexpensively manufactured, and also which provide for the placement of greater amounts of active material in the cell so as to have longer shelf and/or service life.
The prior art includes Daley et al U.S. Pat. No. 3,068,312 issued Dec. 11, 1962, who teach a sealed cell having a conductive container cover which may be metallic and which is fitted into a sealing member having a diaphragm through which a current collect passes. The current collector contacts the underside of the conductive cover. Feldhake, U.S. Pat. No. 3,713,896, issued Jan. 30, 1973, teaches a cell having a cover member where a seal is effected by coating at least a surface of the rim of the member with a resin, and which requires either a spring or a welded member on the underside of the cover member for current collection. Spanur, U.S. Pat. No. 3,802,923, issued Apr. 9, 1974, simply teaches a dry cell having a resealable vent closure which comprises a disc-like cover fitted over the open end of the cell can and including a resilient flapper valve member which is formed at the outer portion of the cover. Decker et al, U.S. Pat. No. 3,994,749, issued Nov. 30, 1976 teach a vent valve for cells including the cover plate for the internal structure of the cell having a central relief apperture. A vent cap is affixed to the cover plate, having one or more vent ports, and a resilient seal is provided between the vent cap and the cover plate to control the release of gasses. Levy, U.S. Pat. No. 4,191,806, issued Mar. 4, 1980, relies on a disc of resilient plastic, with a pressure vent which is a recess having a frangible diaphragm. The Levy structure has no support disc, and requires a mechanically induced stress failure for venting. Hooke et al, in U.S. Pat. No. 4,271,241, issued June 2, 1981, teach a resealable pressure relief vent valve which includes an outer rigid plate and an inner flexible disc which forms part of the interior of the cell can. The disc has one or more vent holes, and there is a compressible rubber disc in partially compressed condition placed between the outer rigid plate and the inner flexible disc and situated over any of the vent holes so as to vent the interior of the cell when the inner flexible disc has flexed upwardly breaking its seal over the holes. One of the principal features of the present invention is to provide a seal that may be fitted to both stepped cell cans and beaded cans, as they may be supplied and manufactured in different regions and in different countries,--and from different can manufacturers--but where the internal assembly of active components is essentially the same.
It is also a purpose of the present invention to provide a design for seals, especially when they are produced from a thermoplastic material such as polypropylene, which permits permeation of hydrogen gas from the cell even when it is in an upside-down position--that is, with the seal in the downmost position.
A further purpose of the invention is to provide such seals in order to assure a good compression force of the member against the inside of the can, so as to even better assure that the cell is well sealed at the crimp.
Safety considerations are also kept in mind by the provisions of the present invention, including safety against outward expulsion of active material in the event of an abrupt vent rupture, and safety against inward intrusion of foreign objects that should not otherwise enter the cell.